Square Column Bench Top Or Knee Mill ?

[GarageWrench]

Ya still getting the just of posting here, forgive me for typing in the copy/paste portion of my post.

 

[wrmiller]

The limited Y axis travel is why I ended up with a 12Z mill. basically a 10x40 table (rounding up .5") and I can get the spindle all the way from the back of the table to two inches off the front or more. And 20" plus of Z which is handy for doing larger stuff. I had a budget as well, but mostly didn't want a machine that I can't move myself because it's too blinkin heavy. The smaller knee mill wasn't too heavy, it just didn't have the Y axis travel I wanted and the table is a bit small. Always tradeoffs when compromising...

If the money and weight wasn't an issue I'd have a 9x49 BP clone with electronic speed control. But for now this mill does everything I need of it. Biggest cut I've done so far is a 1/2" rougher end mill at 1" DOC full width. Worked fine. A little hard on the cutter though, as I don't have a coolant system yet.

 

[GA Gyro]

Interesting dilemma... what machine to get... we all have been there.
IMO the advise of determining the cube size of work you will do (X - Y - Z) would be something to consider; both current work and expanding into future needs.

My vote would be to forget the bed mills and go with a knee mill. I was ready to ask Matt at QMT (Quality Machine Tools, the Precision Matthews machines) to send me a PM932PDF (basically a clone of an RF45)... then at the last minute changed my mind and asked Matt to send me a PM935 (clone of a BP J head). This BP clone cones in two sizes; a 935 or a 949... both have the same 3HP head. The 935 is a bit lighter machine, generally called a 2/3 (or 3/4) BP clone. The 949 is mostly a full sized BP. The advantage of the 935 is weight (around 1600# vs around 2500#), the advantage of the 949 is the machine is more ridged- the ability to take serious roughing cuts. Having said that, I have taken cuts with my 935 that will cause the motor to grunt, so one should not consider the 935 a light-weight by any means.

If it were me, and the space/money were available, I would seriously consider the PM935:
http://www.machinetoolonline.com/PM-935HighPrecisionMills.html

Personally, I bought a 3PH motor belt drive (PM935TS) and put a VFD on it (VFD is a phase inverter, varies the phase to vary speed-- also allows you to run the 3PH motor with single phase current supplied). I am quite happy with my choice.

Lots of folks at this forum have purchase the PM935 series (both TS and TV). With a little searching, you can find many threads of receiving, set up, and impressions of using the machine.

On a side note, lots of those folks that purchased the PM935 also purchased the PM1340GT lathe... the two seem to be a good pair. Again, lots of reviews on this lathe at this forum.

 

[tmarks11]

Yea, my 12Z is what I was referring to.

Whoops, forgot to mention Bill got one too.

Coolidge just sticks in my mind more, since he had to get two..

 

[GarageWrench]

Ya Gyro, I would love to have that PM935, that would eliminate my budget, but I would get the XY and Z to cover all I would need and the ragidaty of the bigger mill. The Grizzly 9901 is also comparable.

I noticed the specs are very similar on the Charter Oak 12 Z and the PM 940m, the Y on both are 12". I don't think PM has shipped that mill as of yet.

In any ones opinion, how important is the auto down feed option on the quill ? Seems as a hobby machinists I could live without that. My mill/drill and lathe are both manual so that's something I'm used to, but I installed a DRO on the Rongfu and would love to have a 3 axis on the new mill (or used mill).

I'm thinking there is a significant loss of ragidaty from the square column to the knee, even the smaller knee's like the Grizzly G0730 style.

Thanks for all the input fellas, great info!

 

[GA Gyro]

Matt's new PM940 is supposed to be in sometime in May... however it seems the freight never gets there on time.

I may have a need for a CNC mill in the future... If I do... I am seriously considering the 940.

And yes, I understand about the $$$ thing. Many of us have joked about totally blowing our budgets (myself included)... yet when we have the machine, we realize it was a wise decision. Note I am not saying to get careless with $$$, just to not be too tight. Future needs seem to always grow into larger machines... just the nature of the beast.

 

[tmarks11]

In any ones opinion, how important is the auto down feed option on the quill ? Seems as a hobby machinists I could live without that.

I am not a big fan of auto-downfeed. I have used it on bridgeport for boring holes. The advantage is that you get a better finish quality using the auto down feed. The BIG disadvantage is the release mechanism that stops the down feed isn't real accurate, so you don't end up with the hole consistently at the depth you want it. Not a big deal if 0.020" is acceptable error. A real big deal if you want to get within 0.005".

I definitely wouldn't pay $300 for this option, unless it is much more accurate than the way that Bridgeport implemented it on their knee mills. And even then, I wouldn't pay $300 for it.

Based upon other's experience with the Charter Oak, I would recommend investigating the PM940 instead. Matt has a good rep on this board (and elsewhere).

 

[JimDawson]

The BIG disadvantage is the release mechanism that stops the down feed isn't real accurate, so you don't end up with the hole consistently at the depth you want it

The trick is to finish the pass manually by pulling the quill down against the hard stop as the feed disengages. It will normally hold better than 0.001.

.

 

[wrmiller]

Ya Gyro, I would love to have that PM935, that would eliminate my budget, but I would get the XY and Z to cover all I would need and the ragidaty of the bigger mill. The Grizzly 9901 is also comparable.

I noticed the specs are very similar on the Charter Oak 12 Z and the PM 940m, the Y on both are 12". I don't think PM has shipped that mill as of yet.

In any ones opinion, how important is the auto down feed option on the quill ? Seems as a hobby machinists I could live without that. My mill/drill and lathe are both manual so that's something I'm used to, but I installed a DRO on the Rongfu and would love to have a 3 axis on the new mill (or used mill).

I'm thinking there is a significant loss of ragidaty from the square column to the knee, even the smaller knee's like the Grizzly G0730 style.

Thanks for all the input fellas, great info!

BP type knee mills are used by smaller shops because they are more 'configurable' with all the tilt and nod capability. Larger shops/factories use 6 and 8 thousand pound (or bigger) Cinci and other brands of bed mills to do any serious stock removal in a production environment. I was talking to a tool and die maker of long experience one day and he described BPs as 'nice hobby machines'.

But we're talking here about hobby use right?

IMO the 935 is one of the highest quality knee mills available in a 3/4 size, but it is a bit spendy for some folks (me included). Matt's new bed mill (PM940) is near identical to my Charter Oak 12Z and if Matt had offered the darn thing when I was shopping I would have bought his instead of the CO just because I have already done business with him and have nothing to say but great things about it (well, other than the waiting around for the machines...but that's NOT Matt's fault). I personally am glad I didn't spend the money on Griz's 695. I think it would have been a great machine, but not quite up to doing some of the things the 12Z can do.

Does Matt have any idea when the new 940s are going to show up? When last I talked to him I was giving him some grief (good naturedly of course) about bringing in all these cool new toys AFTER I go and spend my money on something else.

 

[tmarks11]

The trick is to finish the pass manually by pulling the quill down against the hard stop as the feed disengages. It will normally hold better than 0.001.

The machines I have used (Sharp 1054, brand new) had about 0.010"+ flex in the hard stop. Impossible to get an accurate cut with the quill. Maybe not the norm, but it was the norm on every machine in the shop.